The bulk of the milestone hour is devoted to a "Sliding Doors" plot — in which McGarrett (Alex O'Loughlin) is kidnapped by Wo Fat (Mark Dacascos) and experiences what his life would have been like if his father, John McGarrett (William Sadler), had never died. And it's a must-see episode for longtime fans, who will finally get a definitive answer as to the exact link between McGarrett and Wo Fat.
So what does Johnny Moreau have to do with all this? TVGuide.com chatted with Rossdale about his guest-starring role, which TV shows he's addicted to, and whether we'll be seeing any more of him on The Voice this season.
Bush played a concert for Hawaii Five-0 earlier this year, but how did your guest appearance come about?
Gavin Rossdale: I don't know. I was asking my manager the same question. It came up and they said, 'Would you like to be in Hawaii Five-0 and would you like to play for them on the beach?' I was like, 'Sure, sounds great.' It was really exciting to do and exciting to go to Hawaii and try and keep up with those good actors on that show. They've had such a very strong run. ... All I'm thinking to myself is, don't mess it up.
So what can you tell us about "the nefarious Johnny Moreau"?
Rossdale: I just play the most double-crossing jerk-off kind of criminal imaginable, because [he] betrays [his] own. I kept on thinking, well, wherever he's got to, he must be pretty charming — a sort of mixture of psychopathic, self-serving, and yet has an ability to break through people. So I kind of figured that a bit of charm was OK, [rather] than a straight out-and-out thug. So I tried to give him a little bit of that dichotomy, that sort of conflict.
Will we be seeing more of him down the road?
Rossdale: I think the idea was that if I didn't mess it up, I might come back. It was an introductory role.
You've been in a number of TV shows and movies. At this point, which do you find more creatively fulfilling: acting or music?
Rossdale: Obviously with the music thing, that's really the mainstay of my existence. That is me, inside and out. And what I love about the acting is that, unlike the music, where I start with a blank page, I get to do this and I just get to interpret someone else's creativity, try and add layers to that. So it's just an interesting process for me.
Will we see you back on The Voice this season, maybe performing?
Rossdale: I hope so. It's like Hawaii Five-0. Until they ask me, I can't say if I'm going back. ... It'd be nice. That is an incredible platform on The Voice. But if that was just my time on it, then that's cool. I really enjoyed it. I wish them all well. Everyone was so gracious there that it was a really good experience.
What TV shows are you enjoying personally?
Rossdale: There's so many shows I can't keep up with. Everyone's going on about this show, that show, and I feel like I'm a cultural dead end because I can only manage to see some of them, and it just drives me mad. But it's really good, and really useful for the bus. Binge-watching on the bus, going to the next show, that's where it really comes into its own.
I've really fallen in love with The Knick. I think that's a staggering show. I love Clive Owen. He's just brilliant, and Steven Soderbergh. ... It's just so incredible. I love that show. It's gory. But then again, so is Game of Thrones. I started watching with Gwen [Stefani, his wife] and everyone's getting their hands chopped off, their feet chopped off. I was like, oh, my God. And now, it's rolled off down the hill away from me and I just can't take it. ... It's become this huge powerhouse, so I feel guiltily behind the times with that. So that's something I need to watch. I enjoyed Orange Is the New Black. That was a really good show. House of Cards is incredible. Also Boardwalk Empire. That is just amazing. I love Shameless. Incredible show. Shameless is the first time I've ever seen an adaptation from an English show that really was just equally as brilliant, in its own way. Emmy Rossum and William H. Macy are just staggering.
Do you have any other TV appearances lined up?
Rossdale: Sadly, not as of yet. But you know, right after this article comes out, I'm expecting a flood of inquiries.
Check out a sneak peek of Rossdale as Johnny Moreau:
Hawaii Five-0 airs Fridays at 9/8c on CBS.
(Full disclosure: TVGuide.com is owned by CBS.)